The invention relates to a method and a device for evaluating electrocardiograms (EKG) in the area of extrasystoles.
Extrasystoles are heartbeats that occur prematurely outside the regular base rhythm; they may occur individually, in twos as so-called couplets or in groups as salvos. According to the location of their origin, the extrasystoles are basically divided into vestibular or supra-ventricular extrasystoles and ventricular extrasystoles. Even today, cause and origin of extrasystoles are still not entirely understood. There is a complex interaction of local factors (in the heart muscle) and overriding structures (in the autonomous nervous system).
Extrasystoles are classified by their type, the frequency of their occurrence, their form and their location of origin. The detection of frequent and repetitive extrasystoles has gained a certain importance in estimating the prognosis of persons who had just undergone a heart attack. However, the detection of extrasystoles in long-term EKGs is not very specific; extrasystoles do not only occur in ill persons but also in healthy ones. It is therefore difficult, if not impossible to derive at therapeutic consequences, for example the prophylactic implantation of a cardio-vortex defibrillator, from an extrasystole for individual patients. Other available methods of risk stratification are relatively unreliable as well. It would be great progress if the individual risk could be determined more accurately than before using parameters that are coupled with extrasystoles.
It is therefore, the principal objective of the invention to specify a method and a device for evaluating electrocardiograms in the area of extrasystoles in order to provide parameters that can be related to the individual risk of a person.
This objective is accomplished according to the invention for a method and a device of the referenced type which caries out the following steps:
(a) after recognizing an extrasystole, determining characteristic attributes of at least the heartbeats occurring in a continuous sequence following the extrasystole, and
(b) quantifying these attributes using an analysis method.
It has been found that extrasystoles leave characteristic signatures in the base rhythm that can be used for risk stratification. For persons with a normal or slightly increased risk, as a rule, the heart beat sequence following an extrasystole usually accelerates, but only for a few heartbeats (transient frequency increase), which is then followed by a phase of frequency decrease of the heartbeat sequence. The heart frequency then levels off to its initial level after about ten to twenty heart actions (transient frequency decrease, see FIG. 3). For persons with an increased risk, this characteristic reaction is significantly weaker or missing altogether. In these cases, often a more or less erratic heartbeat sequence, that is, one without order, can be found.
Basically, various options are available to quantify these differences, for example using analysis methods in the time or frequency domains.
Using the time domain, the following parameters have proven useful in estimating the risk:
xe2x80x9cOnsetxe2x80x9d: Difference of the mean values of the last normal RR intervals preceding the extrasystole and the first normal RR intervals following the extrasystole; preferably, two RR intervals each immediately preceding and following the extrasystole are used.
xe2x80x9cSlopexe2x80x9d: Greatest frequency decrease within a sequence of several, e.g., 20 heart beat intervals determined following an extrasystole across, preferably, five successive RR intervals as slope of the regression line.
xe2x80x9cCorrelation coefficient of the slopexe2x80x9d: A measure for the regularity of the slope and generated by numeric mean value generation of several successive slope values.
All quantities mentioned have proven suitable for risk stratification: With a small onset, a flat slope or a low correlation coefficient of the slope, the risk of dying in the continued course is significantly increased. With a considerable onset, steep slope or high correlation coefficient of the slope, the risk is normal or significantly lower.
In the frequency domain, the low- or high-frequency portions can be quantified and their ratio can be determined: When the high-frequency portions increase, the risk of dying in the continued course is higher. If the low-frequency portions increase, the risk is normal or significantly lower.
In a multi-variant analysis, the new risk parameters proved to be largely independent of all other risk parameters used thus far. This means, that a significant portion of the information contained in them is indeed new, that is, clinically additive.
When investigating the vestibular extrasystoles, such associations of the slope and the correlation coefficient of the slope with the mortality risk were found as well.
A device for evaluating electrocardiograms in the area of extrasystoles can also be integrated directly in an instrument for recording the electrocardiograms, particularly long-term electrocardiograms. This instrument then not only provides the actual EKG, but also the evaluation with regard to the time behavior of the heartbeats preceding and following an extrasystole. The integration of such a device according to the invention into a pacemaker or into an implanted defibrillator is conceivable as well.
In general, extrasystoles are easily recognized in an EKG, because the time behavior andxe2x80x94in the case of the ventricular extrasystolesxe2x80x94its shape changes visibly compared to the regular base rhythm. Thus, a sequence preceding an extrasystole can be clearly differentiated from a sequence following an extrasystole.
It is, otherwise, also possible to use the method according to the invention for clinical research regarding the effect of medication. It has been found that with the help of onset, slope and correlation coefficient of the slope, patients with varying effects of an antiarrhythmic medication can be identified. The more pronounced the onset, slope and correlation coefficient are in the treatment of patients, the more effective the medication will be classified.
For a full understanding of the present invention, reference should now be made to the following detailed description of the preferred embodiments of the invention as illustrated in the accompanying drawings.